This invention relates to a reactive ion etching (RIE) apparatus for producing, for instance, semiconductor devices, and more particularly for etching anisotropically various types of thin films which constitute an integrated circuit in a plasma space.
A conventional type of RIE apparatus has a reaction chamber having an exhaust means and a gas leading-in means, and also a pair of electrodes therein facing each other, in which plasma is generated by supplying a high frequency electrical field to said pair of electrodes therein and a thin film placed on one of said electrodes as an object to be processed is etched in said plasma space.
In the case where such a conventional RIE apparatus is used, in order to set a condition for an etching process such as, for instance, an etching speed, the following types of data correlated to an etching speed are collected prior to the etching process; the quantity of a gas fed into a reaction chamber, an exhaust speed in said reaction chamber, and an output from a high frequency power supply. With these various types of data, factors for determining an etching speed are controlled indirectly by using an experimenter's sense of experience. Referring to FIG. 9 which shows an example of such types of data, the etching speed (A/min) is plotted along the ordinate against an output from a high frequency power supply (W) which is plotted along the abscissa, with three resulting curves each corresponding to the pressure (85, 300, 500 mTorr) in a reaction chamber used as a parameter.
Other conditions for an etching process include conditions to minimize damages to a base material and those to select a base material and a material to be etched. In any of the cases using these conditions, a complicated method as described above is used to set each condition for an etching process.
Another known method is that a probe is inserted in a plasma space during an etching process to observe the state of ions in the plasma which heavily affects the etching process in order to change each condition.
However, with a conventional RIE apparatus having the structure as described above, two much time and labor are consumed to set conditions for an etching process.
Furthermore, those methods are based on indirect control, which makes improvement in its precision difficult. For instance, when a probe is inserted, it may cause disturbance in said plasma or contamination on an object to be processed.
For the above-described reasons, the structure based on the prior art as described above hinders the work from being processed smoothly or the quality of an object to be processed from being improved. The prior art can not be applied to work in an actual industrial production site to obtain satisfactory results, although it may produce tolerable results in a laboratory.
Regarding RIE, it is well known that ions bombarded to a surface to be etched, or more particularly the energy and the quantity of ions bombarded to a surface to be etched, play important roles in an etching process, and yet a practical method for directly controlling these physical quantities has not yet been found.
The purpose of this invention is to provide an RIE device, wherein conditions for an etching process such as an etching speed can be set easily, precisely and with a high reliability. To accomplish this object, this invention adopts a new concept, the flow rate of charged particles, which is a quantity proportional to the quantity of bombarded ions and can directly be measured.